1. Field of the Invention
The present invention relates generally to electron beam apparatus equipped with high-brightness electron sources and, more particularly, to electron beam apparatus adaptable for use with equipment with built-in electron guns utilizing Schottky emission effects and also a high-voltage discharge prevention method thereof.
2. Description of the Related Art
While electron beam apparatus requires the use of an electron gun for taking an electron beam out of it, a high-voltage cable which is inserted from ambient air side into a high-voltage introduction insulator unit of the electron gun for supplying a filament heat-up current and/or a high voltage to an electron source is typically attached. However, if water content or moisture resides in a gas (typically air) which is present on the surface of this high-voltage introduction insulator and the surface of a high-voltage cable and also in a gap between the both, then discharge can take place in high-voltage application events resulting in destruction of the electron source. To avoid this, in the prior art, a dryer is used to sufficiently dry the surfaces of the high-voltage introduction insulator and high-voltage cable to thereby retain enhanced air-tightness between them for prevention of entry of wet air from the outside into the gap therebetween.
With the electron gun of the above-stated prior art electron beam apparatus, it is difficult to maintain the required air-tightness for an increased length of time period at the junction portion of an electrical conductive portion and a dielectric portion (mold material) of the high-voltage cable even when the electron gun is designed to prevent entry of any moisture from the outside upon insertion of the high-voltage cable into the high-voltage introduction insulator side under ambient air pressures. Due to this, there has been a problem which follows: with elapse of time, moisture-containing air enters into the gap between the high-voltage introduction insulator and the high-voltage cable resulting in an increase in amount of water content, which sometimes leads to ionization during high-voltage application causing discharge or generation of a leakage current, resulting in damages of the electron source and/or decreases in stability of a beam current.